1. Field of the Invention
The present invention relates to vulcanization accelerators consisting of compounds belonging to the group of enamines.
More specifically, the present invention relates to vulcanization accelerators consisting of compounds, deriving from primary or secondary aliphatic amines, belonging to the group of enamines and a process for their preparation.
2. Discussion of the Background
It is known that the vulcanization of natural or synthetic rubbers takes place by the cross-linking between polymeric chains owing to the use of sulfur or peroxides.
The vulcanization process in the presence of sulfur has been optimized by the use of accelerators capable of limiting the vulcanization times and guaranteeing repeated results with respect to the properties of the end-products.
There are many known products which are used as vulcanization accelerators as described, for example, by Kirk-Othmer: "Encyclopedia of Chemical Technology", Vol. 20, pages 337-364. Among these mercaptobenzothioazol and its sulfenamides, dithiocarbamates and thiuram disulfides, can be mentioned.
Frequently, in order to obtain good results, these products are not used alone but are combined with each other.
Among vulcanization accelerators there is a group of products defined as secondary accelerators, used as activators of primary accelerators with a thiazole base. Examples of these products are: N,N'-diphenylguanidine (DPG), N,N'-diortho-toluylguanidine (DOTG), 2,4,6-tris-dimethylaminomethylphenol and the condensation products of aromatic amines with aliphatic aldehydes.
European patent application 634.448, filed by the Applicant, describes vulcanization accelerators consisting of compounds belonging to the group of enamines having the following general formula: ##STR2##
wherein:
R'.sub.1 and R'.sub.2, the same or different, represent a C.sub.1 -C.sub.18 alkyl group, linear or branched; a C.sub.2 -C.sub.18 alkenyl group; a C.sub.3 -C.sub.8 cycloalkyl group; a C.sub.6 -C.sub.18 aryl group; a C.sub.7 -C.sub.20 alkylaryl or arylalkyl group; or R'.sub.1 and R'.sub.2, considered jointly with the nitrogen atom, represent a C.sub.3 -C.sub.8 heterocyclic group possibly containing a second heteroatom selected from O, S and N; PA1 R'.sub.3 and R'.sub.4, the same or different, represent a hydrogen atom; a C.sub.1 -C.sub.18 alkyl group, linear or branched; a C.sub.2 -C.sub.18 alkenyl group; a C.sub.6 -C.sub.18 aryl group; a C.sub.7 -C.sub.20 alkylaryl or arylalkyl group; or R'.sub.3 and R'.sub.4, considered jointly with the double bond C.dbd.C to which they are linked, represent a C.sub.3 -C.sub.12 cycloalkenyl group; PA1 R'.sub.5 represents a hydrogen atom; a C.sub.1 -C.sub.18 alkyl group, linear or branched; a C.sub.2 -C.sub.18 alkenyl group; or, when R'.sub.3 represents a hydrogen atom, a linear or branched C.sub.1 -C.sub.18 alkyl group, a C.sub.2 -C.sub.18 alkenyl group, a C.sub.6 -C.sub.18 aryl group or a C.sub.7 -C.sub.20 alkylaryl or arylalkyl group, R'.sub.4 and R'.sub.5, considered jointly with the carbon atom which has the double bond C.dbd.C, represent a C.sub.3 -C.sub.12 cycloalkylene group. PA1 R.sub.1 and R.sub.2, the same or different, represent a hydrogen atom; a C.sub.1 -C.sub.18 alkyl group, linear or branched; a C.sub.2 -C.sub.8 alkoxyalkyl group, linear or branched; a C.sub.3 -C.sub.8 cycloalkyl group possibly containing a heteroatom selected from oxygen, nitrogen and sulfur; a C.sub.7 -C.sub.20 arylalkyl group; or R.sub.1 and R.sub.2, considered jointly with the nitrogen atom, represent a C.sub.3 -C.sub.8 heterocyclic group possibly containing a second heteroatom selected from oxygen, nitrogen and sulfur; PA1 R.sub.3 represents a C.sub.1 -C.sub.18 alkyl group, linear or branched; a C.sub.6 -C.sub.18 aryl group; a C.sub.7 -C.sub.20 alkylaryl or arylalkyl group; a C.sub.1 -C.sub.8 alkoxyl group linear or branched.
The Applicant has now found compounds, deriving from primary or secondary aliphatic amines, belonging to the group of enamines, which can be used as vulcanization accelerators and have improved properties with respect to those known in the art. In fact, the above enamines are less volatile, are not irritating and generally have no odour.